1. Field of the Invention
This invention relates to an organopolysiloxane composition comprising fluorosilicone-treated silica compounded therein, and also relates to a process for preparing the composition.
2. Description of the Prior Art
Silica fine powder is compounded into organopolysiloxane compositions such as silicone rubbers, silicone greases, and silicone oil compounds, for the purpose of controlling fluidity, reinforcing mechanical strength, improving release properties or adhesion, and also improving compression set, thermal resistance and chemical resistance.
Silica fine powders used for such purpose include fumed silica and wet-processed silica. These silica fine powders, however, all have a number of silanol groups on their particle surfaces. Hence, the compounding of such silica fine powder into organopolysiloxane as it is may cause the pseudo-crosslinking called structuring or creep hardening, during the storage of the resulting compositions. This may result in an extreme lowering of the fluidity or consistency of the compositions, bringing about the problem of plasticization reversion occurring in an excessively great extent particularly in the case of rubber compositions.
Under such circumstances, it has been hitherto attempted to use surface-treated silica, obtained by applying surface treatment to the above silica fine powders so that the silanol groups on the particle surfaces are hindered by silylation, thereby avoiding the above problems.
Methods for such surface treatment of silica fine powder are known to include a method in which silica fine powder is reacted with chlorosilane or a silazane compound, and a method in which silica fine powder and silicone rubber are kneaded and thereafter the above silazane compound, or a dialkylsilanediol, an alkoxysilane or the like is added to carry out reaction.
The release properties and transparency, however, have been unsatisfactory in the above organopolysiloxane compositions in which the conventional surface-treated silica is compounded.